cloudflare-to-bun

Cloudflare Workers to Bun Migration

You are assisting with migrating Cloudflare Workers applications to Bun. This involves converting edge runtime APIs, replacing Cloudflare bindings, and adapting from edge to server deployment.

Quick Reference

For detailed patterns, see:

• Runtime APIs: runtime-apis.md - Cloudflare to Bun API mapping
• Bindings Migration: bindings.md - KV, R2, D1, Durable Objects replacements
• Deployment: deployment.md - Edge to server deployment strategies

Migration Workflow

1. Pre-Migration Analysis

Check current setup:

# Check Cloudflare CLI
wrangler --version

# Check Bun installation
bun --version

# Analyze wrangler.toml
cat wrangler.toml

Review worker configuration:

# Check compatibility flags
grep compatibility_flags wrangler.toml

# Check bindings
grep -E "kv_namespaces|r2_buckets|d1_databases|durable_objects" wrangler.toml

2. Worker Types Analysis

Determine what type of Worker you're migrating:

• Service Worker: Traditional addEventListener('fetch') format
• Module Worker: Modern export default { fetch() } format
• Scheduled Worker: Cron triggers
• Durable Objects: Stateful objects
• Pages Functions: Next.js-like file-based routing

3. Runtime API Conversion

Basic Fetch Handler

Cloudflare Worker (Module format):

export default {
  async fetch(request: Request, env: Env, ctx: ExecutionContext): Promise<Response> {
    return new Response('Hello World');
  },
};

Bun Server:

Bun.serve({
  port: 3000,
  fetch(request: Request): Response | Promise<Response> {
    return new Response('Hello World');
  },
});

console.log('Server running on http://localhost:3000');

Request/Response Handling

Cloudflare Worker:

export default {
  async fetch(request: Request): Promise<Response> {
    const url = new URL(request.url);

    if (url.pathname === '/api/data') {
      return Response.json({ data: 'value' });
    }

    return new Response('Not found', { status: 404 });
  },
};